Image heating apparatus

ABSTRACT

An image heating apparatus for heating a toner image formed on a recording material is constituted by a roller contactable with a toner image carrying surface of the recording material; a heating member for heating the roller, the heating member contacting a surface of the roller, wherein the toner image formed on the recording material is heated in contact with the roller; and a driving mechanism for moving the heating member to a first position contacting the roller and a second position, contacting the roller different from the first position with respect to a tangential direction of the roller.

FIELD OF THE INVENTION AND RELATED ART

The present invention relates to an image heating apparatus suitable fora heat-fixing device mounted to a copying machine or a printer,particularly an image heating apparatus including a roller contactablewith a toner image and a heating member contacting a surface of theroller.

U.S. Pat. No. 6,763,205 (Japanese Laid-Open Patent Application (JP-A)2003-186327) has proposed a constitution in which a roller contacting atoner image is heated from a surface side of the roller and heataccumulated at the roller surface is imparted to the toner image to heatthe toner image. An image heating apparatus of this type (externalheating type) is not required to be warmed at an inner portion of theroller so that it has an advantage such that thermal capacity is low andthus electric power consumption can be reduced.

The external heating type image heating apparatus is classified into aconstitution in which the heating member contacts the roller and aconstitution in which the heating member does not contact the roller.The contact type image heating apparatus is preferable to thenon-contact type image heating apparatus since it has better heattransfer efficiency from the heating member to the roller.

However, in the case of the contact type image heating apparatus, therearises such a problem that toner transferred from a recording materialonto the roller is liable to be deposited on the heating member.Agglomerative toner deposited and grown considerably is abruptlydischarged onto the roller surface to cause a problem of contaminationor the like of the recording material during a heating step of the tonerimage. When a cleaner for removing the toner deposited on the heatingmember is provided, a cost is increased correspondingly.

U.S. Pat. No. 7,190,914 (JP-A 2005-250452) has disclosed a technique inwhich a heating member is heated in a state in which rotation of aroller to be heated by the heating member is stopped and thereaftertoner deposited on the heating member is fixed on the roller by coolinga heating area to remove the toner from the heating member. Further,U.S. Pat. No. 7,155,136 (JP-A 2005-250453) has disclosed a technique inwhich a roller to be heated by a heating member is rotated normally andreversely in a heated state of the heating member to wipe the tonerdeposit on the heating member with the toner.

SUMMARY OF THE INVENTION

In view of the above described circumstances, a principal object of thepresent invention is to provide an image heating apparatus capable ofmore effectively removing toner deposited on a heating member comparedwith the conventional techniques.

Another object of the present invention is to provide an image heatingapparatus capable of removing toner deposited in the neighborhood of anedge of the heating member.

According to an aspect of the present invention, there is provided animage heating apparatus for heating a toner image formed on a recordingmaterial, comprising:

a roller contactable with a toner image carrying surface of therecording material;

a heating member for heating the roller, the heating member contacting asurface of the roller,

wherein the toner image formed on the recording material is heated incontact with the roller; and

a driving mechanism for moving the heating member to a first positioncontacting the roller and a second position, contacting the rollerdifferent from the first position with respect to a tangential directionof the roller.

These and other objects, features and advantages of the presentinvention will become more apparent upon a consideration of thefollowing description of the preferred embodiments of the presentinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an image forming apparatus in which theimage heating apparatus according to the present invention is mounted asa fixing apparatus.

FIG. 2 is a constitutional view of an image forming apparatus inEmbodiment 1.

FIG. 3 is a flow chart showing an operation of an image formingapparatus in Embodiment 1.

FIGS. 4( a) and 4(b) are schematic views showing positionalrelationships between a heating member and a fixing roller when thefixing roller is rotated normally (FIG. 4( a)) and reversely (FIG. 4(b)).

FIGS. 5( a) and 5(b) are schematic views showing positionalrelationships between a heating member and a fixing roller when thefixing roller is rotated normally (FIG. 5( a)) and reversely (FIG. 5(b)).

FIG. 6 is a constitutional view of an image heating apparatus inEmbodiment 2, wherein a fixing roller is rotated normally.

FIG. 7 is a constitutional view of an image heating apparatus inEmbodiment 2, wherein the fixing roller is stopped.

FIG. 8 is a schematic view for illustrating toner contamination in theneighborhood of a heat nip.

FIG. 9 is a flow chart showing an operation of an image formingapparatus in Comparative Embodiment.

FIG. 10 is a constitutional view of an image heating apparatus inEmbodiment 3.

FIG. 11 is a front view of the image heating apparatus in Embodiment 3.

FIG. 12 is a schematic view showing a heating member driving mechanismof the image heating apparatus in Embodiment 3.

FIG. 13 is a schematic view showing a state in which a heating member ismoved in a direction opposite from a rotational direction of a fixingroller in Embodiment 3.

FIG. 14 is a schematic view showing a state in which the heating memberis moved in the same direction as the rotational direction of the fixingroller in Embodiment 3.

FIG. 15 is a schematic view showing a deposition state of toner leadingto toner contamination in an image heating apparatus to which a heatingmember is fixed.

FIG. 16 is a schematic view showing a state in which a contaminantlocated downstream from a contact heating portion is moved in thecontact heating portion.

FIG. 17 is a schematic view showing a state in which the contaminantmoved in the contact heating portion is transferred onto the fixingroller.

FIG. 18 is a graph showing a relationship between a conveying timing ofa recording material and a reciprocating timing of a heating member.

FIG. 19 is a constitutional view of an image heating apparatus inEmbodiment 4.

FIG. 20 is a front view of the image heating apparatus in Embodiment 4.

FIGS. 21 and 22 are schematic views each showing a process oftransferring a contaminant deposited on a heating member onto a fixingroller in Embodiment 4.

FIG. 23 is a constitutional view of an image heating apparatus inEmbodiment 5.

FIG. 24 is a top view of the image heating apparatus in Embodiment 5.

FIGS. 25 and 26 are schematic views each showing a process oftransferring a contaminant deposited on a heating member onto a fixingroller in Embodiment 5.

FIG. 27 is a constitutional view of the image heating apparatus inEmbodiment 6.

FIG. 28 is a sectional view of an image forming apparatus in which animage heating apparatus is mounted as a fixing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

An image heating apparatus according to the present invention will bedescribed with reference to the drawings. FIG. 1 is a schematic view ofan image forming apparatus to which the image heating apparatus of thepresent invention is mounted. Referring to FIG. 1, the image formingapparatus in this embodiment is a laser beam printer utilizing atransfer type electrophotographic process.

The image forming apparatus includes image forming means including aprocess cartridge 73, a laser scanner 3, a transfer roller 5, and aheat-fixing apparatus 6. The process cartridge 73 is detachably(replaceably) mountable to a main assembly of the image formingapparatus. In this embodiment, the process cartridge 73 includes fourprocess means consisting of an electrophotographic photosensitive member1 (hereinafter referred to as a “photosensitive drum”), a chargingroller 2, a developing apparatus 4, and a cleaning apparatus 7. Thephotosensitive drum 1, the charging roller 2, and a developing roller inthe developing apparatus 4 are rotated by receiving power from a motorMO1. The main motor MO1 also drives rollers or the like for conveying arecording material. In the laser scanner 3, a polygon mirror forperforming polarization scanning of laser light is provided and isrotated by receiving power from a scanner motor mounted in the laserscanner 3.

The photosensitive drum 1 is prepared by forming a photosensitivematerial such as an organic photoconductor (OPC), amorphous selenium(Se), or amorphous silicon (Si) on a cylindrical substrate of aluminumor nickel. The photosensitive drum 1 is rotationally driven in aclockwise direction indicated by an arrow at a predetermined peripheralspeed and electrically charged uniformly to a predetermined polarity anda predetermined potential by the charging roller 2 as a chargingapparatus.

Thereafter, with respect to the charged surface of the photosensitivedrum 1, light exposure for writing image information is performed by thelaser scanner 3. More specifically, the laser scanner 3 performsscanning exposure of the uniformly charged surface of the photosensitivedrum with a laser beam L which is ON/OFF-controlled(modulation-controlled) depending on a time-serial electrical digitalpixel signal as the image information. As a result, a potential of alight exposure portion at the uniformly charged surface of thephotosensitive drum 1 is attenuated, so that an electrostatic latentimage corresponding to the image information is formed on the surface ofthe photosensitive drum 1.

The electrostatic latent image is developed as a toner image by thedeveloping apparatus 4. As a developing method, a jumping developingmethod, a two-component developing method, an FEED developing method, orthe like is used. In many cases, a combination of imagewise lightexposure and a reverse developing method is employed.

The toner image is transferred from the surface of the photosensitivedrum 1 onto a surface of a recording material PA fed to a transfer nipA. The transfer nip A is a press-contact portion between thephotosensitive drum 1 and the transfer roller 5 as a contact transferapparatus contacting the photosensitive drum 1. The recording materialPA is fed from an unshown feeding mechanism portion to the transfer nipA at predetermined timing. More specifically, the timing is adjusted bydetecting a leading end of the recording material PA with a sensor 8 sothat an image forming position of the toner image on the photosensitivedrum 1 coincides with a writing position of the leading end of therecording material PA. The recording material PA fed at thepredetermined timing is nipped and conveyed in the transfer nip Abetween the photosensitive drum 1 and the transfer roller 5 with acertain pressing force, so that the toner image on the surface of thephotosensitive drum 1 is transferred onto the recording material PA byan electric force and a pressure.

The recording material PA passing through the transfer nip A isseparated from the surface of the rotating photosensitive drum 1 andconveyed to the heat-fixing apparatus 6 in which an unfixed toner imageis heat-fixed as a permanent image on the recording material surface.The recording material PA subjected to the image fixation is conveyed toa sheet discharge portion.

Transfer residual toner remaining on the photosensitive drum 1 after theseparation of the recording material therefrom is removed from thesurface of the photosensitive drum 1 by the cleaning apparatus 7 and thephotosensitive drum 1 is repetitively subjected to image formation.

[Heat-Fixing Apparatus (Image Heating Apparatus) 6]

FIG. 2 is an enlarged schematic view of the heat-fixing apparatus 6 inthis embodiment. As shown in FIG. 2, the heat-fixing apparatus 6 isroughly constituted by a fixing roller 10, a heating member 20contacting a surface of the fixing roller 10, and a pressing member 30.The fixing roller 10 is rotated by receiving power from a motor MO2 fora fixing unit. The fixing unit motor MO2 is a motor capable of beingrotated normally and reversely, thus being rotatable in a rotationaldirection during fixation (normal rotation) (in X1 direction indicatedby an arrow in FIG. 4( a)) and in a direction (reverse rotation) in X2direction indicated by an arrow in FIG. 4( b)).

The fixing roller 10 has an elastic layer. The heating member 20contacts the fixing roller 10 to form a heating nip H, thus heating thefixing roller 10. The pressing member 30 and the fixing roller 10mutually contact to form a fixing nip (conveying nip) N. The heating nipis an area in which the fixing roller 10 and the heating member 20contact each other, and the fixing nip is an area in which the fixingroller 10 and the pressing member 30 contact each other.

The heating member 20 is held in a recess of a holder 24 for holding theheating member 20. The heating member 24 is fixed to a main assembly ofthe heat-fixing apparatus 6 so as not to move both in L1 direction andin L2 direction. Further, the fixing roller 10 is also fixed to the mainassembly of the heat-fixing apparatus 6 in a rotatable state so as notto move both in the L1 and L2 directions.

In the recess of the holder 24, a gap G1 (FIG. 4( a)) and 4(b)) isprovided between the heating member 20 and the holder 24 so that theheating member 20 is movable in the L1 and L2 directions in the recessof the holder 24.

[Fixing Roller 10]

The fixing roller 10 is basically prepared by subjecting an outersurface of a core metal 11 formed of aluminum or iron tosurface-roughening process such as blasting and thereafter providing anelastic layer 12 on the outer surface of the core metal 11.

The elastic layer 12 is a sponge rubber layer of foamed silicone rubberor a foam rubber layer including a silicone rubber layer and hollowfiller dispersed therein, thus being improved in a heat insulatingfunction by ensuring a gas portion in the rubber layer.

When the fixing roller 10 has a larger thermal capacity and any largerthermal conductivity, the fixing roller 10 is liable to absorb thereinheat from the outer surface of an external heating member 21, so that asurface temperature of the fixing roller 10 is less liable to beincreased. For this reason, the elastic layer 12 is formed of a materialsuch that it has a thermal capacity and a thermal conductivity as low aspossible and has a high heat insulating effect, so that a rise time ofthe fixing roller 10 is shortened.

The thermal conductivities of the sponge rubber and the foam rubber are0.10-0.16 W/(m·k), which is about half of that of a solid rubber. Valuesof specific gravity, associated with the thermal capacity, of the spongerubber and the foam rubber are about 0.75-0.85. Accordingly, in apreferred embodiment, the elastic layer 12 of the fixing roller 10 is asponge rubber layer or foam rubber layer having a low thermalconductivity of 0.15 W/(m·k) or less and a high heat insulating effectin terms of specific gravity of 0.85 or less.

A small outer diameter of the fixing roller 10 can be effective insuppressing the thermal capacity but when the outer diameter isexcessively small, the widths of the heating nip and fixing nip are lessliable to be ensured. For this reason, the fixing roller 10 requires aproper outer diameter. With respect to the thickness of the elasticlayer 12, a proper thickness is required since an excessively smallthickness leads to dissipation of heat into the core metal 11.

In view of the above requirements, in this embodiment, the elastic layer12 is formed of a foam rubber layer having a thickness of 2 mm and afixing roller 10 having an outer diameter of 14 mm is used in order toform a proper heat nip H and suppress the thermal capacity.

As the hollow filler in the core metal 11, it is possible to use anymaterial, such as glass balloon, silica balloon, carbon balloon, phenolballoon, acrylonitrile balloon, vinylidene chloride balloon, aluminaballoon, zirconia balloon, or Shirasu balloon.

The core metal 11 may also be a hollow core metal. On the elastic layer12, a heat transfer layer 12 b (solid rubber layer) which is formed ofsilicone rubber and has a heat transfer effect is disposed. The heattransfer layer 12 b has a thermal conductivity of 0.50-1.60 W/(m·k) anda specific gravity of about 1.05-1.30.

In the case where the heat transfer layer 12 b has a small thickness,the heat transfer effect and the heat capacity are decreased, so that aheat accumulating effect is not achieved. On the other hand, when thethickness is increased, the heat accumulating effect and the heattransfer effect are achieved but heat from a heat generating element 22is conducted to the inside of the fixing roller 10, thus beingaccumulated in the fixing roller 10 to lead to a poor thermalefficiency. Accordingly, the thickness of the heat transfer layer 12 bmay preferably 0.1-0.30 mm, more preferably about 0.15 mm.

On the heat transfer layer 12 b, a parting layer 13 formed of afluorine-containing resin material such as perfluoroalkoxy (PFA) resin,polytetrafluoroethylene (PTFE) resin, ortetrafluoroethylene-hexafluoropropylene (FEP) resin is formed.Alternatively, it is possible to effect coating of the heat transferlayer 12 b with GLS latex. The parting layer 13 may have a tube-likeshape or may be coated with paint.

[Heating Member 20]

The heating member 20 includes a plate-like substrate 21 and a heatgenerating resistor 22 formed on the substrate 21. The substrate 21 isan insulating ceramic substrate formed of alumina or aluminum nitride ora heat resistive substrate formed of polyimide, PPS, a liquid crystalpolymer, etc. The heat generating resistor 22 is, e.g., prepared bycoating a surface of the substrate 21 with a paste of a material such asilver-palladium (Ag/Pd), RuO₂, or TaN along a longitudinal direction ofthe substrate 21 by screen printing and thereafter sintering the paste.The heat generating resistor 22 has an elongated shape having athickness of about 10 μm, a width of about 1-5 mm, and a length of about300 mm.

The heating member 20 may further include a protective layer 23 forprotecting the heat generating resistor 22 within bounds of notimpairing the thermal efficiency. However, the thickness of theprotective layer 23 may preferably be a sufficient small to the extentthat a surface property is improved. Examples of the protective layer 23may include a layer of fluorine-containing resin such as perfluoroalkoxy(PFA) resin, polytetrafluoroethylene (PTFE) resin,tetrafluoroethylene-hexafluoropropylene (FEP) resin,ethylenetetrafluoroethylene (ETFE) resin, polychlorotrifluoroethylene(CTFE) resin, and polyvinylidene fluoride (PVDF), which are coatedsingly or in mixture. Alternatively, it is also possible to use aprotective layer formed of a dry coating lubricant such as graphite,diamond-like carbon (DLC), or molybdenum disulfide, and formed of aglass coating material.

In the case where aluminum nitride or the like having a good thermalconductivity is used as a material for the substrate 21, the heatgenerating resistor 22 may also be formed on the substrate 21 at asurface opposite from a surface facing the fixing roller 10.

In this embodiment, the substrate 21, the heat generating resistor 22,and the protective layer constitute one component, i.e., a heater 20.Thus heater 20 directly contacts the fixing roller 10 to form theheating nip (heating area) H.

The heating member holder 24 is formed of a heat resistive resinmaterial such as a liquid crystal polymer, phenolic resin, PPS, or PEEK,and a thermal efficiency with respect to heat at the fixing rollersurface is increased with a decreasing thermal conductivity. Thus, theheating member holder 24 may also contain hollow filler such as glassballoon or silica balloon in the resin layer.

In the heater 20, a temperature detecting device 14 such as a thermistorfor detecting a temperature of the heating member 20 is disposed at asurface opposite from the surface facing the fixing roller 10. Thetemperature detecting device 14 is provided for the purpose ofcontrolling the temperature of the heating member 20 or monitoringabnormal temperature rise of the heating member 20.

When the temperature detecting device 14 is used for temperaturecontrol, depending on a signal from the temperature detecting device 14,a duty ratio or a wave number of a voltage applied from an unshownelectrode portion at a longitudinal end portion to the heat generatingresistor 22 is appropriately controlled. As a result, the heatgenerating resistor 22 is heated to heat and temperature-control thesurface of the fixing roller 10.

[Pressing Member 30]

The pressing member 30 is prepared by adhering a heat resistive sheet 31b to a heat resistive pad 31 c.

The heat resistive sheet 31 b is a film-like sheet having a heatresistivity and a slidability and has an appropriate thickness in arange of 20 μm or more and less than 200 μm in view of a film strengthor the like.

On a surface of the sheet 31 b, it is also possible to coat a layer of aheat resistive resin material, having good releasability andslidability, such as PFA, PTFE, FEP, or silicone resin, singly or inmixture. As a result, offset toner deposited on the fixing roller 10 canbe efficiently removed with reliability, so that it is possible toobtain a good image by suppressing contamination of the fixing roller10.

The pressing member 30 is mounted in a recess of a holder TS fixed to aframe of the fixing apparatus. In the recess, a gap G2 (FIGS. 5( a) and5(b)) is provided between the pressing member 30 and the holder TS sothat the pressing member 30 is movable in the recess in a direction (M1direction in FIG. 2) identical to the recording material conveyingdirection and an opposite direction (M2 in FIG. 2). Further, thepressing member 30 is pressed against the fixing roller 10 together withthe holder TS by an unshown urging means, so that the fixing nip Nrequired for fixation is created between the pressing member 30 and thefixing roller 10.

The pad 31 c holds the heat resistive sheet 31 b and is suitably formedwith a member having the heat resistivity and slidability including theheat resistive resin material such as the liquid crystal polymer, thephenolic resin, PPS, or PEEK.

[Operation of Heat-Fixing Apparatus]

In the above-constituted heat-fixing apparatus 6, the fixing roller 10is rotationally driven in a clockwise direction indicated by an arrow(X1 direction) during fixation with the core metal 11 as a rotationalaxis in a longitudinal direction thereof. Further, by energizing theheat generating resistor 22, the heater 20 is quickly increased intemperature. The energization of the heat generating resistor 22 iscontrolled by a control circuit including the temperature detectingdevice 14 so that the heater 20 is kept at a predetermined (set)temperature.

By the heat generation of the heat generating resistor 22, the outersurface of the fixing roller 10 is heated. It is also possible to heatthe fixing roller 10 through a sheet-like sliding member disposedbetween the outer surface of the fixing roller 10 and the heater 20.However, the constitution of omitting the sliding member can provide aninexpensive heat-fixing apparatus. In the case where the heater 20directly contacts the fixing roller 10 as in this embodiment, the heater20 corresponds to the heating member. On the other hand, in the casewhere the sliding member is interposed between the heater 20 and thefixing roller 10, the heater 20 and the sliding member constitute theheating member in combination or the sliding member alone constitutesthe heating member.

In such a state, the recording material PA on which the unfixed tonerimage is formed and carried is conveyed, along a fixing entrance guide15, to the fixing nip N created between the fixing roller 10 and thepressing member 30. Then, the unfixed toner image on the recordingmaterial PA is fixed by heat and pressure.

A difference between the above described heat-fixing apparatus 6 and aheat-fixing apparatus of Comparative Embodiment will be described. FIG.8 is en enlarged view showing a heating portion (a contact area Hbetween a fixing roller 100 and a heater 230) and its neighborhood ofthe heat-fixing apparatus in Comparative Embodiment.

In the case where toner T which cannot be fixed on the recordingmaterial is located on the surface of the fixing roller 100, the toner Tvan be deposited on a contact surface of the heating member 230press-contacting the fixing roller 100 or at an upstream side endportion or a downstream-side end portion.

As shown in FIG. 8, a deposition portion of the toner T can be locatedin a contact area S or principally located in an area K at thedownstream-side end portion of the heating member 23 with respect to therotational direction of the fixing roller 100. In this state, when thefixation of the toner image is continued, the toner T deposited on theheating member 230 somewhat rubs the fixing roller surface, thus alwaysleading to contamination of the fixing roller 100.

Further, the toner T deposited on the heating member 230 intimatelycontacts and rubs the fixing roller 100 to damage of the surface of thefixing roller 100 with respect to a circumferential direction of thefixing roller 100.

Further, large agglomerative toner T deposited in the area K can cause adefective image by accidentally falling on the recording material. Thereason why the toner is liable to be deposited in the K is that arelative positional relationship between the heating member 230 and thefixing roller 100 is always fixed and a rotational direction of thefixing roller 100 is always the same direction.

FIG. 9 is a flow chart showing a print sequence of an image formingapparatus to which the heat-fixing apparatus in Comparative Embodimentis mounted. Referring to FIG. 9, in the sequence in ComparativeEmbodiment, an operation which is called premulti-rotation forperforming initial checking of an apparatus itself immediately afterelectric power is turned on is effected (S1 and S2). Thepremulti-rotation is a rotation operation of a photosensitive member 1or the fixing roller 100 performed during a preparatory operation fromturning-on of a printer until the printer is placed in a printablestate. During the premulti-rotation, a main motor and a motor for afixing unit are started to be rotated, so that the fixing roller 100 isrotated in a direction in which the recording material PA is conveyed.At the same time as the operation, energization of the heating member230 is also started, so that the heating member 230 is increased intemperature up to a set temperature suitable for a fixing process. Thisset temperature is ordinarily in a range of 150-210° C. After thepremulti-rotation is completed, the image forming apparatus is in astandby state in the case of no print signal (print instruction), sothat the main motor and the fixing unit motor are stopped until theprint signal is provided. At the same time, the energization of theheating member 230 is also completed (S3 to S5).

When a print start instruction is provided from a host computer, thesequence goes to pre-rotation which is an operation for print (S6). Whenthis operation is started, the rotation operations of the main motor andthe fixing unit motor are started and at the same time, energization ofthe heating member 230 is also started. At this time, the heating member230 is kept at a set temperature capable of fixing the toner on therecording material while being subjected to temperature detection by thetemperature detection device 14.

When the preparation of the printer is completed, the recording materialis fed by a feeding roller and a toner image is transferred onto therecording material at a transfer portion, and the recording material isconveyed to the heat-fixing apparatus.

When the fixing process is completed, the sequence goes to apost-processing sequence of the apparatus which is called post-rotation(S7). The post-processing sequence is an operation for scraping thetoner T remaining on the photosensitive drum and cooling the heat-fixingapparatus. In the case where this operation is completed, rotations ofthe main motor and the fixing unit motor are stopped and the imageforming apparatus is returned to the state immediately after theelectric power is turned on.

The above sequence is described for an ordinary print operation statebut in other states in which a jam occurs and continuous printing isperformed, a sequence in which the main motor and the fixing unit motorare stopped (S8 to S10).

This Embodiment

Next, a print sequence of an image forming apparatus to which theheat-fixing apparatus of this embodiment is mounted will be described.FIG. 3 is a flow chart showing the print sequence in this embodiment.FIG. 4( a) is a schematic view showing a positional relationship betweenthe heater 20 and the fixing roller 10 when the fixing roller 10 isnormally rotated (X1 direction) and a positional relationship betweenthe heater 20 and the holder 24. FIG. 4( b) is a schematic view showinga positional relationship between the heater 20 and the fixing roller 10when the fixing roller 10 is reversely rotated (X2 direction) and apositional relationship between the heater 20 and the holder 24.

Referring to FIG. 3, the heat-fixing apparatus 6 is characterized inthat the heater 20 is moved in L2 direction by reversely rotating thefixing unit motor MO2 in a small amount after the fixing unit motor MO2is stopped (S41 and S42). Incidentally, the main motor is not rotatedreversely.

In the sequence of this embodiment, during the motor stop (after S4)after the premulti-rotation performed during the turning-on of electricpower, the fixing unit motor MO2 is reversely rotated (S41). Further,during the motor stop (after S10) after the post-rotation performedafter completion of the print, the fixing unit motor MO2 is reverselyrotated (S42).

During the premulti-rotation or the fixing process after electric powerof the printer is turned on, the fixing roller 10 is rotated in X1direction shown in FIG. 4( a). Since the gap G1 is preset between theholder 24 and the heater 20, so that the heater 20 is moved in L1direction when the fixing roller 10 is heated in X1 direction. When thefixing roller 10 is continuously rotated in X1 direction, the toneroffset from the recording material PA onto the surface of the fixingroller 10 is gradually deposited at a position (area) K shown in FIG. 4(a).

However, in this embodiment, the gap G1 is provided between the holder24 and the heater 20 as described above and the fixing roller 10 isreversely rotated (X2 direction) to move the heater 20 in L2 directionas shown in FIG. 4( b). By this movement, the toner deposited in thearea K enters the area of the heating nip H to melt the toner by heat ofthe heater 20 at predetermined timing to return the toner to the fixingroller 10, so that the toner is prevented from excessively depositing onthe heater 20.

Here, assuming that the position of the heating member shown in FIG. 4(a) is a first position and the position of the heating member shown inFIG. 4( b) is a second position, the heating member is moved to thefirst position at which it contacts the fixing roller 10 and the secondposition, at which it contacts the fixing roller 10, different from thefirst position in tangential direction of the fixing roller 10. Thesecond position is located upstream from the first position with respectto the rotational direction of the fixing roller 10 during the tonerimage heating.

In this embodiment, the fixing roller 10 is rotatable normally (X1direction) and reversely (X2 direction). This fixing roller 10 functionas a part of the driving mechanism for moving the heating member, sothat the heating member is moved to the first position or the secondposition depending on a force receiving from the fixing roller 10. Theheating member is located at the first position during the toner imageheating and moved from the first position to the second position inperiods (e.g., during print signal receiving and during standby stateafter the printing) other than the heating period.

In this embodiment, the fixing unit motor is reversely rotated so thatthe heater 20 is moved by a distance of the gap G. In this embodiment,the heating nip has a width of about 3 mm with respect to the rotationaldirection of the fixing roller 10 and the gap G is 1 mm. Even when theheater 20 is moved 1 mm, the heat generating resistor 22 of the heater20 does not come out of the heating nip H.

As described above, the heating member is held by the holder and betweenthe holder and the heating member, the gap for moving the heating memberto the first position and the second position is provided.

The heating member includes the substrate and the heat generatingresistor formed on the substrate and the heat generating resistor isconstituted so as not to come out of the contact area between theheating member and the fixing roller both at the time when it is locatedat the first position and at the time when it is located at the secondposition.

As shown in FIG. 4( b), the area K is moved within the heat nip H by thereverse rotation performed immediately after the motor stop. In otherwords, the contact area of the heater 20 with the fixing roller 10 isdifferent between during the normal rotation and during the reverserotation.

When the heater 20 is moved to the position shown in FIG. 4( b), theheat-fixing apparatus is stopped but thereafter when the print signal isprovided, energization of the heat generating resistor 22 is started atthe same time as the motor rotation. At this time, toner or paper dustdeposited on the heater (heating member) side in the area K istransferred to the fixing roller side. This is because the heater sidesurface of the toner sandwiched between the heater 20 and the fixingroller 10 is heated by the heater 20 for a fraction of time to bemelted, thus being lowered in deposition force with respect to theheater.

When the recording material PA reaches the fixing nip N, the tonercontinuously conveyed by the rotation of the fixing roller while beingdeposited on the fixing roller surface is transferred and fixed onto theupper surface of the conveyed recording material PA to be discharged outof the heat-fixing apparatus. By moving the heater 20 to the positionshown in FIG. 4( b) every time when the premulti-rotation afterturning-on of the power of the printer is completed or when the fixingprocess operation (printing operation) is completed, a resultant imageis not adversely affected by the toner or paper dust deposited on therecording material since an amount of the toner or paper dust depositedon the heater 20 in the area K is very small.

By repeating this sequence, the area K of the heater 20 is kept good, sothat a good image is printed.

However, the above-described reverse rotation sequence is not alwaysperformed when the motor is stopped. In an emergency stop state such asjamming or the like, the reverse rotation sequence must not beperformed. For example, in the emergency stop state, in the neighborhoodof the fixing nip N, unfixed toner in a state in which both heat andpressure have not been applied is located in some cases. In such cases,when the reverse rotation sequence is performed, a large amount of theunfixed toner is deposited on the fixing roller surface, so that thereis a possibility that the unfixed toner adversely affects the fixingroller 10 and the heater 20.

Here, a state after the reverse rotation sequence will be described. Inthis embodiment, by performing the reverse rotation sequence, the heater20 is moved about 1.0 mm. However, by normally rotating the fixingroller after the reverse rotation sequence, the amount of movement isreset, so that the position of the heater 20 is returned to the ordinaryposition at which the heater 20 is located before the reverse rotation.

The change in position of the heater 20 by the normal rotation and thereverse rotation is due to its frictional force against the fixingroller 10.

[Fixing Pressing Member]

The fixed pressing member 30 as a fixed backup means will be described.The fixed pressing member also slidably contacts the fixing roller 10and is constituted so that the recording material PA is conveyed betweenthe fixed pressing member and the fixing roller 10.

As described above, on the surface of the pressing member 30, thefluorine-based sheet having good releasability is provided but the toneris deposited with an increase in number of printed sheets, so that thepressing member 30 is contaminated in some cases.

However, basically, the toner deposited on the pressing member isdischarged as a small contaminant while being gradually deposited on aleading end of the recording material PA by causing the recordingmaterial PA to pass between the fixing roller 10 and the pressing member30. Thus, the discharged toner is not recognized as image failure on therecording material. Further, the amount itself of the toner deposited onthe pressing member is very small.

Nevertheless, the toner is deposited on the pressing member 30. In theone-directional rotation sequence as in Comparative Embodiment,similarly as in the case of the heater 20, the toner is deposited on thepressing member 30 on a downstream side with respect to the rotationaldirection of the fixing roller 10 (a position P shown in FIG. 5( a)) inmany cases. The thus deposited toner is still remaining on the pressingmember 30 without being removed by the recording material PA. The tonerdeposited at the position P impairs conveyance of the recording materialPA and can cause jamming (an abnormal state in which the recordingmaterial remains in the heat-fixing apparatus and cannot be outputted).

In this case, by using the reverse rotation sequence, it is possible toremove the deposited toner similarly as in the case of removing thetoner from the heater 20. The pressing member is movable by a small gapG2 during the reverse rotation of the fixing roller 10 since the gap G2is provided between the pressing member 30 and the holder TS. In thisembodiment, the fixing nip N has a width of 3 mm and the gap G2 is 1.0mm.

FIG. 5( a) is a schematic view showing a positional relationship betweenthe pressing member 30 and the fixing roller 10 when the fixing roller10 is normally rotated (X1 direction) and a positional relationshipbetween the pressing member 30 and the holder TS. FIG. 5( b) is aschematic view showing a positional relationship between the pressingmember 30 and the fixing roller 10 when the fixing roller 10 isreversely rotated (X2 direction) and a positional relationship betweenthe pressing member 30 and the holder TS.

As shown in FIG. 3, the fixing unit motor MO2 is reversely rotatedduring the motor stop (after S4) after the premulti-rotation performedafter turning-on of electric power and during the motor stop (after S10)after the post-rotation performed after completion of the printing (S41and S42).

As shown in FIGS. 5( a) and 5(b), by reversely rotating the motor MO2,the pressing member 30 is moved from the position shown in FIG. 5( a) tothe position shown in FIG. 5( b). An amount of this movement is equal tothe value of the gap G2.

As shown in FIG. 5( a), an area P in which toner or paper dust isdeposited is located on a downstream side of the pressing member 30 withrespect to the rotational direction of the fixing roller 10. This toneris the residual toner which cannot be completely fixed on the recordingmaterial PA and deposited on the pressing member 30.

The area P is moved within the fixing nip N by the reverse rotationperformed immediately after the motor stop (S41, S42), as shown in FIG.5( b).

When the print is started in a state in which the pressing member islocated at the position shown in FIG. 5(B), the toner deposited on thepressing member is removed by rubbing with the fixing roller 10. Thethus removed toner deposited on the fixing roller 10 is transferred ontothe upper surface of the recording material PA and fixed thereon.

By frequently performing the above described reverse rotation, an amountof the toner or paper dust deposited in the area P is very small, sothat an image quality is not remarkably lowered even when the effecttoner is deposited on the recording material PA. As a result, byperforming the reverse rotation in this embodiment, it is possible tosuppress an occurrence of jamming by suppressing accumulation of thetoner or paper dust in the area P.

However, similarly as in the case of moving the heater 20, theabove-described reverse rotation sequence is not always performed whenthe motor is stopped. In an emergency stop state such as jamming or thelike, the reverse rotation sequence must not be performed. For example,in the emergency stop state, in the neighborhood of the fixing nip N,unfixed toner in a state in which both heat and pressure have not beenapplied is located in some cases. In such cases, when the reverserotation sequence is performed, a large amount of the unfixed toner isdeposited on the fixing roller surface and the pressing member surface,so that there is a possibility that the unfixed toner adversely affectsthe fixing roller 10 and the pressing member 30.

In the case of emergency stop such as jamming or the like, the electricpower is turned on, i.e., the premulti-rotation is performed ordinarilyafter the jammed paper is removed. In this state, there is no recordingmaterial on which unfixed toner is carried in a large amount, so thatthe unfixed toner is not deposited on the fixing roller surface and thepressing member surface even when the reverse rotation is performed.

Here, a state after the reverse rotation sequence will be described. Inthis embodiment, by performing the reverse rotation sequence, thepressing member 30 is moved about 1.0 mm. However, by normally rotatingthe fixing roller after the reverse rotation sequence, the amount ofmovement is reset, so that the position of the pressing member 30 isreturned to the ordinary position at which the pressing member 30 islocated before the reverse rotation.

The change in position of the pressing member 30 by the normal rotationand the reverse rotation is due to its frictional force against thefixing roller 10.

In this embodiment, the non-rotatable pad-shaped pressing member 30 isused but the pressing member 30 may also be a rotatable roller. When thepressing member is the rotatable roller, a latitude for thecontamination is basically increased.

Embodiment 2

An image heating apparatus of this embodiment will be described. FIG. 6is a constitutional view showing the image heating apparatus of thisembodiment in which a fixing roller 10 is placed in a rotating state.FIG. 7 is a constitutional view showing the image heating apparatus ofthis embodiment in which the fixing roller 10 is not rotated. Members ormeans identical to those employed in Embodiment 1 are represented byidentical numerals or symbols and a redundant explanation will beomitted.

As shown in FIG. 6, in the image heating apparatus of this embodiment,springs (urging members) 41 and 42 for moving the heater 20 and thepressing member 30 are provided in place of the reverse rotationsequence employed in Embodiment 1. As a result, withoutreversely/rotating the fixing unit motor, it is possible to suppress thedeposition of the toner in the heater 20 and the pressing member 30 withan inexpensive constitution. A driving mechanism for moving the heatingmember (heater) to a first position (FIG. 6) and a second position (FIG.7) includes the fixing roller 10 for moving the heating member to thefirst position and the urging member for moving the heating member tothe second position. Although described specifically later, the heatingmember in this embodiment is moved to the first position against anurging force of the urging member by receiving a force from the fixingroller by rotation of the fixing roller and moved to the second positionby the urging force when the rotation of the fixing roller is stopped.

In a specific constitution, similarly as in Embodiment 1, a gap isprovided between the heater 20 and the heating member holder 24 forholding the heater 20. The gap is 1.0 mm. On the other hand, a gap isalso provided between the pressing member 30 and the holder TS forholding the pressing member 30. The gap is also 1.0 mm. When the fixingroller 10 is rotated, the heater 20 and the pressing member 30 overcomethe urging forces of the springs 41 and 42 to be moved to the positionshown in FIG. 6, so that a gap (spacing) S1 (=1 mm) and a gap S2 (=1 mm)are created at upstream-side portions with respect to the rotationaldirection of the fixing roller 10.

The spring 41 urges the heater 20 toward the upstream portion withrespect to the rotational direction of the fixing roller 10. The spring41 is compressed by the movement of the heater 20 when the fixing roller10 is rotated. In this embodiment, a pressing force from the heater 20to the fixing roller 10 is 2.0 kgf (19.6 N), so that a load of about 2.0kgf (19.6 N) is applied to the spring 41 by a frictional force betweenthe fixing roller 10 and the heater 20.

The spring 42 urges the pressing member 30 toward the upstream portionwith respect to the rotational direction of the fixing roller 10. Thespring 42 is compressed by the movement of the pressing member 30 whenthe fixing roller 10 is rotated. In this embodiment, a pressing forcefrom the pressing member 30 to the fixing roller 10 is 2.0 kgf (19.6 N),so that a load of about 1.5 kgf (14.7 N) is applied to the spring 41 bya frictional force between the fixing roller 10 and the pressing member30.

As shown in FIG. 7, in the case where the fixing roller 10 is stopped,there is no frictional force received from the fixing roller 10. Inaddition, compression forces of the springs 41 and 42 are released,whereby the heater 20 and the pressing member 30 are moved in adirection of increasing the gap on the downstream side with respect tothe rotational direction of the fixing roller 10 to be returned to thestates before the rotation of the fixing roller 10 (returned from thestate of FIG. 6 to the state of FIG. 7).

In this embodiment, similarly as in Embodiment 1, a fixing rollercontact area of the heater 20 and a fixing roller contact area of thepressing member 30 are different between during rotation of the fixingroller 10 and during stop of the fixing roller 10. For this reason,toner or paper dust deposited on the heater 20 and the pressing member30 can be deposited on the fixing roller 10, thus being discharged afterbeing transferred onto the recording material PA. As a result, it ispossible to suppress an occurrence of an offset image and image failurecaused due to damage and wearing of the roller and falling of thedeposited toner.

Further, it is also possible to suppress an amount of the tonerdeposited on the heater and the pressing member, so that it is possibleto prevent shortening of lifetime due to a lowering in driving torqueand wearing. In this embodiment, in addition to the effects achieved inEmbodiment 1, it is not necessary to perform the reverse rotationsequence, so that a throughput can be improved.

In this embodiment, the spring 41 has a force of 1.8 kgf (17.6 N) andthe spring 42 has a force of 1.4 kgf (13.7 N). These forces may bechanged since a constitutional state of the image heating apparatusvaries largely depending on the pressing forces and the materials of thecoating and the sheet.

Next, embodiments in which the heating member is moved from the firstposition to the second position during the toner image heating tosuppress deposition of the toner on the heating member will bedescribed.

Embodiment 3

In this embodiment, first, a constitution of a main assembly of an imageforming apparatus to which an image heating apparatus of the presentinvention is mounted will be described and then a fixing apparatus towhich the image heating apparatus is applied will be described.

[Main Assembly Constitution]

In this embodiment, ordinary method and apparatus for forming an unfixedtoner image on the recording material are employed and will be describedwith reference to FIG. 28.

Referring to FIG. 28, an image forming apparatus 50 in this embodimentemploys a method in which toner images of four colors of yellow,magenta, cyan, and black are successively transferred onto a recordingmaterial P carried on a recording material conveying belt 9 to form oneimage. Around a peripheral surface of a photosensitive drum 1, a charger2, an exposure device 3 for irradiating the photosensitive drum 1 withlaser light, a developing device 5, a transfer roller disposed via therecording material conveying belt, and a photosensitive drum cleaner 16are disposed in this order with respect to a rotational directionindicated by an arrow R1. First, a surface of the photosensitive drum 1is electrically charged to a negative polarity by the charger 2. On thesurface of the charged photosensitive drum 1, an electrostatic latentimage is formed by exposure to light L by the exposure device 3 sincethe exposed portion is increased in surface potential. At theelectrostatic latent image portion on the photosensitive drum 1, toneris deposited by the developing device 5 containing first yellow toner toform a yellow toner image.

The recording material conveying belt 9 is supported by two supportingshafts (a driving roller 12 and a tension roller 14) and rotated in adirection indicated by an arrow R3 by the driving roller 12 rotating ina direction indicated by an arrow R4. The recording material P iselectrically charged by an adsorption roller 6 to which apositive-polarity bias is applied when the recording material P is fedby a sheet feeding roller 4, and is electrostatically adsorbed andconveyed on the recording material conveying belt 9. When the recordingmaterial P is conveyed to a transfer nip N1, a positive-polaritytransfer bias is applied from an unshown power source to the transferroller 10 rotated by the recording material conveying belt 9, so thatthe yellow toner image on the photosensitive drum 1 is transferred ontothe recording material P in the transfer nip N1. From the surface of thephotosensitive drum 1 after the transfer, transfer residual toner isremoved by the photosensitive drum cleaner 16 having an elastic blade.

A series of image forming processes including the above describedcharging, exposure, developing, transfer, and cleaning is successivelyperformed with respect to respective developing cartridges M30 forsecond color of magenta, C30 for third color of cyan, and K30 for fourthcolor of black to form four color toner images in total on the recordingmaterial P carried on the recording material conveying belt 9. Therecording material P carrying thereon the four color toner images areconveyed to a fixing apparatus 100, in which fixation of the surfacetoner images is effected.

[Fixing Apparatus]

The fixing apparatus 100 in this embodiment will be described. Thefixing apparatus 100 in this embodiment in a surface image heatingapparatus of a sliding contact type for reducing a rise time andelectric power consumption. FIG. 10 is a schematic sectional viewshowing the fixing apparatus in this embodiment. In contact with anouter peripheral surface of a fixing roller (rotatable member) 110, aheater 112 as a heating unit (heating member) is disposed to form acontact heating portion (heating area) N1. On the other hand, a pressingroller 111 contacts the fixing roller 110 to form a fixing nip N2.

The fixing roller 110 has an outer diameter of 20 mm and is prepared byforming a 4 mm-thick elastic layer 116 (foamed silicone rubber layer) onan outer surface of an iron-made core metal 117 having a diameter of 12mm. When the fixing roller 110 has a large thermal capacity and a largethermal conductivity, the fixing roller 110 is liable to absorb thereinheat received through the outer peripheral surface thereof, thus beingless increased in surface temperature. In other words, it is possible toreduce a rise time of the surface temperature of the fixing roller 110when the fixing roller 110 has thermal capacity and conductivity as lowas possible and is formed of a material having a high heat insulatingeffect. The foamed silicone rubber has a thermal conductivity of0.11-0.16 W/m·K lower than that (0.25-0.29 W/m·K) of a solid rubber.With respect to a specific gravity associated with the thermal capacity,the solid rubber has a specific gravity of about 1.05-1.30, whereas thefoamed silicone rubber has a specific gravity of about 0.75-0.85, thushaving a low thermal capacity. Accordingly, this foamed silicone rubberis capable of shortening the rise time of the surface temperature of thefixing roller 110. A small outer diameter of the fixing roller 110 iseffective in suppressing the thermal capacity but an excessively smallouter diameter leads to a small width of the contact heating portion N1,so that the fixing roller 110 requires a proper outer diameter and thushas an outer diameter of 20 mm in this embodiment. Also with respect toa thickness of the elastic layer 116, a proper thickness is requiredsince an excessively thin elastic layer leads to dissipation of heatinto the iron-made core metal and thus is 4 mm in this embodiment. Onthe elastic layer 116, as a parting (release) layer of toner, a partinglayer 118 formed of perfluoroalkoxy (PFA) resin is disposed. The partinglayer 118 may be prepared by coating the elastic layer 116 with a tubeor paint. In this embodiment, the tube excellent in surface durabilityis employed. In addition to PFA, as the material for the parting layer118, it is also possible to use a fluorine-containing resin materialsuch as polytetrafluoroethylene (PTFE) resin ortetrafluoroethylene-hexafluoropropylene (FEP) resin; fluorine-containingrubber and silicone rubber excellent in parting property; and the like.A surface hardness of the fixing roller 110 can ensure a width of thecontact heating portion N1 even at a low pressure when it is small butan excessively small surface hardness impairs surface durability. Forthis reason, in this embodiment, the fixing roller has a surfacehardness of 40-45 degrees in terms of Asker-C hardness (under a load of4.9 N). The fixing roller 110 is rotated in a direction indicated by anarrow R2 at a surface moving speed of 60 mm/sec by an unshown rotatingmeans.

The pressing roller 111 may preferably have a low thermal capacity and alow thermal conductivity so as not to draw heat from the fixing roller110 and has the same constitution as that in Embodiment 1. The pressingroller 111 has an outer diameter of 20 mm and is prepared by forming a 4mm-thick foamed rubber elastic layer 122 on an outer surface of aniron-made core metal 121 having a diameter of 12 mm. The pressing roller111 has a parting layer 123 formed of PFA as an outermost layer. Thepressing roller 111 is pressed against the fixing roller 110 at a forceof 147N in a direction indicated by an arrow A1 by a pressing rollerpressing spring 124 via a bearing 125 to form the fixing N2 having awidth of 7 mm and is rotated in a direction indicated by an arrow A3 bythe fixing roller 110.

The heating unit 112 is constituted by a heater (heating element) 113 asa heating source, a heater holder 119 for holding the heater 113, and aheat sliding layer 120 contacting the heater 113. The heating unit 112is pressed against the fixing roller 110 at a force of 117.6N in adirection indicated by an arrow A1 by a pressing spring 114 to form thecontact heating portion N1 having a width of 8 mm with respect to thefixing roller rotational direction. The heater 113 includes an aluminasubstrate, a heat generating resistor layer formed on the substrate, anda protective layer. The substrate has a width of o12 mm with respect tothe fixing roller rotational direction and a thickness of 1 mm. The heatgenerating resistor layer is formed of silver-palladium (Ag/Pd) in asize of 4 mm in width and 10 μm in thickness at a central portion of thesubstrate by screen printing. The protective layer is formed of glass ina thickness of 50 μm. The surface of the fixing roller 110 may be heatedby causing the glass surface of the heater 113 to directly contact thesurface of the fixing roller 110 but in this embodiment, the heatsliding layer excellent in parting property and slidability is providedon the surface of the heater 113. This heat sliding layer 120 not onlysuppresses deposition of the offset toner from the surface of the fixingroller 110 to the heating unit 112 but also reduces a frictional forceby rubbing with the fixing roller 110. As a material for the heatsliding layer 120, it is possible to use a fluorine-containing resinsuch as PFA excellent in parting property with respect to toner or PTFEexcellent in slidability. An excessively thick heat sliding layer 120 isless liable to transfer heat from the heater 113 to the fixing roller110 and an excessively thin heat sliding layer 120 has a poor surfacedurability, so that the thickness of the heat sliding layer 120 maypreferably be about 1-100 μm. Further, the heat sliding layer 120 maypreferably have a sheet shape excellent in durability and surfaceproperty. In the case of the sheet shape, the heat sliding layer 120 canbe disposed to cover upstream and downstream edge portions of the heater113, so that the fixing roller 110 is advantageously protected fromdamage by the edges of the heater 113. In this embodiment, as the heatsliding layer 120, a 50 μm-thick PFA sheet is used and disposed to coverthe edges of the heater 113. At a rear surface of the heater 113, atemperature detecting device 115 for detecting a rear surfacetemperature of the ceramic substrate increased in temperature dependingon heat generation of energized heat generating resistor layer isdisposed. The temperature of the heater 113 is adjusted by appropriatelycontrolling a current flowing from an unshown electrode portion disposedat a longitudinal end portion of the heater 113 to the energized heatgenerating resistor layer depending on a signal from the temperaturedetecting device 115. The heater 113 heats the surface of the fixingroller 110 in an area of the contact heating portion N1.

When the recording material P onto which the unfixed toner image T istransferred is conveyed to the fixing nip N2 by an unshown conveyingmeans, heat at the surface of the fixing roller 110 is transferred tothe unfixed toner image and the recording material P to fix the tonerimage T on the recording material P.

Next, a constitution, as a feature of the present invention, in whichthe heating unit is moved will be described. In the sliding contact typesurface image heating apparatus in this embodiment, the heating memberis moved in a direction opposite from the fixing roller rotationaldirection at the contact heating portion. The fixing apparatus in thisembodiment is provided with a heat element swingable cam 141 for movingthe heating unit 112 (the heater 113) in an opposite direction from thefixing roller rotational direction. A front view of the fixing apparatusas seen from a direction indicated by an arrow A3 in FIG. 10 is shown inFIG. 11. The cam 141 is provided about a cam shaft 128 at bothlongitudinal end portions of the heating unit 112. A cam rotation gear126 provided at an end portion of the cam shaft 128 is rotationallydriven by an unshown driving means to rotate the came 141 in a directionindicated by an arrow R4.

FIG. 12 is an enlarged view of the contact heating portion and itsneighborhood. When the fixing roller 110 is rotated in the arrow R2direction, the heating unit 112 receives a force in a direction of anarrow A4 (the same direction as the fixing roller rotational direction)by friction with the fixing roller 110 at the contact heating portionN1. The heat unit 112 in this embodiment is movable in directionsidentical to and opposite from the fixing roller rotational direction.For this reason, when the fixing roller 110 is rotated in the arrow R2direction to apply the force to the heating unit 112 in the arrow A4direction, the heating unit 112 is placed in a contact state with thecam 141. In this state, a center line C2 of the heating unit (thesubstrate of the heater) is located at a position (first position) movedfrom a center line C1 of the fixing roller 110 by W1=2 mm. The cam 141has a larger radius with an increasing degree of phase shift in an arrowR5 direction. For this reason, when the cam 141 is rotated in an arrowR4, the heat unit 112 is pushed and moved in a direction opposite fromthe surface moving direction A4 thereof (the fixing roller rotationaldirection) at the contact heating portion N1. The cam 141 in thisembodiment has such a shape that the radius is smoothly increased fromminimum radius R1=10 mm to a maximum radius R2=14 mm by 4 mm duringrotation up to ¾ turn (270 degrees). The cam 141 pushes and moves theheating unit 112 by 4 mm in the opposite direction from the fixingroller rotation direction by being rotated, in the arrow R4 direction by270 degrees, from the position of the minimum radius (R1=10 mm) shown inFIG. 12 to the maximum radius (R2=14 mm) shown in FIG. 13 at the contactportion with the heating unit 112. As shown in FIG. 13, when the heatingunit 112 is moved from the position shown in FIG. 12 by 4 mm in theopposite direction from the fixing roller rotational direction, thecenter line C2 of the heating unit 112 is located at a position (secondposition) moved in the opposite direction from the fixing rollerrotational direction with a distance W2=2 mm from the center line C1 ofthe fixing roller 110.

When the cam 141 is further rotated and located at a position shown inFIG. 14, a radius of the cam 141 at the contact portion with the heatingunit 112 is again the minimum radius R1=10 mm. For this reason, theheating unit 112 is moved in the identical direction to the fixingroller rotational direction while contacting the cam 141 to be returnedto the position shown in FIG. 12.

More specifically, in the case where the fixing roller 110 is rotated inthe arrow R2 direction, when the cam 141 is rotated in the arrow R4direction, the heating unit 112 is moved to the position shown in FIG.13 and then returned to the position shown in FIG. 12 through theposition shown in FIG. 13, thus being reciprocated. As described above,the driving mechanism in this embodiment includes the cam (member) 141for urging the heating member from the first position to the secondposition, and the heating member is moved to the first position and thesecond position depending on the motions of the fixing roller 110 andthe cam 141.

On the other hand, in a constitution in which a heating unit is fixed soas not to be moved, when continuous printing is performed, a contaminantsuch as paper dust or offset toner is accumulated on the heating unit112 side at the contact heating portion N1 as described above. FIG. 15is a schematic view for illustrating a state of the contaminantaccumulated at the contact heating portion N1 in the constitution inwhich the heating unit is not moved. Referring to FIG. 15, a contaminantY1 remaining at the contact heating portion N1 contains paper dust andoffset toner in mixture, so that it is placed in a melted state by beingrubbed with the fixing roller 110 at the contact heating portion N1. Inthis melted state, the contaminant Y1 passes through the contact heatingportion N1 to be accumulated in a deposition state on the heating unitside located downstream from the contact heating portion N1 (close to anoutlet portion of the contact heating portion N1). When the continuousprinting is further continued, the downstream contaminant Y1 of thecontact heating portion N1 is further deposited to increase a contactarea between the fixing roller 110 and the contaminant Y1. In thisstate, a large amount of the contaminant is transferred from the heatunit 112 to the fixing roller 110, so that a recording materialsubsequently conveyed can be contaminated. Further, in some cases, thecontaminant Y1 located downstream from the contact heating portion N1 isstill accumulated continuously without being transferred onto the fixingroller 110 to enter the contact heating portion N1, so that heatconduction from the heater 113 to the fixing roller 110 can be impairedto cause image failure such as fixation failure.

In this embodiment, as described above, the heating unit 112 is moved inthe opposite direction from the fixing roller rotational direction. Inthe case where the contaminant Y1 is accumulated at a portion downstreamfrom the contact heating portion N1, when the cam 141 is rotated to movethe heating unit 112 in the opposite direction from the fixing rollerrotational direction, the contaminant Y1 enters the contact heatingportion N1 as shown in FIG. 16. At the contact heating portion N1, thesurface of the fixing roller 110 is moved in a direction opposite fromthe arrow A5 direction in which the heating unit 112 is moved. For thisreason, the contaminant Y1 entering the contact heating portion N1 isremoved by rubbing with the fixing roller 110, so that it is possible totransfer the contaminant Y1 onto the surface of the fixing roller 110 asshown in FIG. 17. The contaminant Y1 transferred onto the fixing roller110 is transferred onto the pressing roller 111, which has a lowertemperature than that of the fixing roller 110, when it reaches thefixing nip N2. Thereafter, when the recording material P is conveyed tothe fixing nip N2, the contaminant Y1 on the pressing roller 111 isdeposited on a rear (back) surface of the recording material P to bedischarged. Further, it is also possible to deposit the contaminant Y1on the front (image forming) surface of the recording material P bymoving the heating unit 112 in the opposite direction from the fixingroller rotational direction to transfer the contaminant Y1 onto thesurface of the fixing roller 110 when the recording material P passesthrough the fixing nip N2. As described above, by moving the heatingunit 112 in the opposite direction from the fixing roller rotationaldirection, the contaminant Y1 located downstream from the contactheating portion N1 can be transferred onto the fixing roller 110, sothat it is possible to discharge the contaminant Y1 onto the recordingmaterial P at the fixing nip N2.

The removal of the contaminant Y1 by moving the heating unit 112 in theopposite direction from the fixing roller rotational direction isperformed on the recording material P, so that the removal of thecontaminant Y1 may preferably be performed frequently so that thecontaminant Y1 deposited on the recording material P can beunnoticeable. In this embodiment, during passage of the recordingmaterial P through the fixing nip N2, the heating unit 112 is alwaysmoved in the opposite direction from the fixing roller rotationaldirection so as not to accumulate the contaminant Y1 at the downstreamportion from the contact heating portion N1.

Timing of movement of the heating unit 112 in the opposite directionfrom the fixing roller rotational direction and timing of conveyance ofthe recording material P in this embodiment are shown in FIG. 18. InFIG. 18, a rotation angle (degrees) of the cam 141 is taken as anabscissa and an amount of movement of the heating unit toward anupstream portion by the rotation of the cam is taken as an ordinate. Theposition of heating unit 112 at cam rotation angles of 0 and 360 degreesis as shown in FIG. 12 and at this position, the upstream movementamount (ordinate) is taken as 0 mm. When the cam 141 is rotated and theheating unit 112 is started to move toward the upstream portion, therecording material P is conveyed to the fixing nip N2 to start fixationof the toner image on the recording material P. When the recordingmaterial P passes through the fixing nip N2, the cam 141 is constitutedso as to be rotated in synchronism with the conveyance of the recordingmaterial P so that the heating unit 112 is moved to the upstreamportion. When the passage of the recording material P through the fixingnip N2 is completed, the upstream movement (4 mm) of the heating unit112 is completed. During a period until a subsequent recording materialP is conveyed to the fixing nip N2, the cam 141 is rotated at timingsuch that the heating unit 112 is returned to the original (downstream)portion. In this embodiment, the conveyance of the recording material Pand the rotation of the cam 141 are synchronized, so that the heatingunit 112 is always moved in the opposite direction from the fixingroller rotational direction during the period in which the recordingmaterial P passes through the fixing nip N2. In other words, themovement direction of the heating unit 112 during a period for heating asingle sheet of recording material is only the opposite direction fromthe fixing roller rotational direction. Accordingly, the contaminantsuch as paper dust or offset toner reaching the contact heating portionN1 is always removed by rubbing with the fixing roller 110, so that thecontaminant cannot be accumulated at a portion downstream from thecontact heating portion N1. Further, the contaminant can be dischargedonto the recording material P little by little from a leading end to atrailing end of the recording material P, thus being efficientlydischarged on the recording material P without becoming noticeable.

When the heating unit 112 is moved by about 1 mm or more in the oppositedirection from the fixing roller rotational direction, the contaminantlocated downstream from the contact heating portion N1 can betransferred onto the fixing roller 110. A larger amount of the movementleads to a longer rubbing removal time of the contaminant at the contactheating portion N1 by the fixing roller 110, so that a contaminantremoving effect becomes larger. However, when the energized heatgenerating resistor layer of the heater 113 comes out of the area of thecontact heating portion N1 by moving the heating unit 112 in theopposite direction from the fixing roller rotational direction, thesurface temperature of the fixing roller 110 is lowered. In the casewhere the heating unit 112 is moved in the opposite direction from thefixing roller rotational direction when the toner image is fixed on therecording material P as in this embodiment, the energized heatgenerating resistor layer is required not to come out of the area of thecontact heating portion N1. In this embodiment, in order that theenergized heat generating resistor layer having a width of 4 mm does notcome out of the contact heating portion N1 having a width of 8 mm evenwhen the heating unit 112 is moved, an amount of movement of the heatingunit 121 is set to 4 mm.

As described above, in the constitution of this embodiment, the heatingunit 112 is always moved in the opposite direction from the fixingroller rotational direction during the passage of the recording materialP through the fixing nip N2, the contaminant located downstream from thecontact heating portion N1 can be discharged unnoticeably onto therecording material P. As a result, it is possible to suppress thedeposition of the contaminant at a portion downstream from the contactheating portion N1.

Comparison between the constitution in which the heating unit is movedin the opposite direction from the fixing roller rotational direction asin this embodiment and the constitution (Comparative Embodiment) inwhich the heating unit is fixed so as not to moved is made by performinga continuous printing test. In the continuous printing test, an imagehaving a print ratio of 5% is continuously printed up to 10×10⁴ sheets(lifetime of the image forming apparatus) and the presence or absence ofoccurrence of image failure or fixation failure due to the contaminantaccumulated at the contact heating portion is checked. In theconstitution of Comparative Embodiment, at the time of printing on about500 sheets, a large amount of the contaminant deposited at the contactheating portion was discharged on the fixing roller to cause imagefailure. The image failure successively occurred at a rate of one sheetper about 200 sheets-printing after the printing on 500 sheets and onesheet per about 100 sheets-printing after the printing on about 40,000sheets. Further, after the printing on about 80,000 sheets, fixationfailure due to heat conduction inhibition by the deposition of thecontaminant at the contact heating portion was started to occur. On theother hand, in the constitution of this embodiment, the heating unit isalways moved in the opposite direction from the fixing roller rotationdirection during the passage of the recording material through thefixing nip, so that the contaminant reaching the contact heating portionis always removed by the fixing roller, thus being not accumulated atthe contact heating portion in a large amount. As a result, up to 10×10⁴sheet which is the lifetime the image forming apparatus, image failureand fixation failure due to the contamination of the contact heatingportion did not occur.

In the above described constitution, the timing of conveyance of therecording material P and the timing of movement of the heating unit 112are synchronized so that the heating unit 112 is always moved in theopposite direction from the fixing roller rotation direction during thepassage of the recording material P through the fixing nip N2. However,the timing of moving the heating unit 112 and a speed thereof are notlimited to those described above. When the fixing roller 110 is rotated,it is possible to transfer the contaminant at the contact heatingportion N1 onto the fixing roller 110 by moving the heating unit 112 inthe opposite direction from the fixing roller rotational direction. Forexample, when the recording material P is not caused to pass through thefixing nip N2, the fixing roller 110 is rotated and the heating unit 112may be moved in the opposite direction from the fixing roller rotationaldirection. By transferring the contaminant at the contact heatingportion N1 onto the fixing roller 110 when the recording material P doesnot pass through the fixing nip N2, the contaminant can be transferredfrom the fixing roller 110 onto the pressing roller 111 to be dischargedon the back surface of the recording material P. By frequently removingthe contaminant in such a manner that the heating unit 112 is movedevery fixing the toner image on one sheet of the recording material P,the contaminant can be unnoticeably discharged on the back surface ofthe recording material P. Further, the fixing process is not performedwhen the recording material P does not pass through the fixing nip N2,so that there is no problem even when the temperature of the fixingroller 110 is lowered to the extent that the fixation of the toner imageon a subsequent recording material P can be ensured. For this reason,the movement distance of the heating unit 112 can be increased with anincreasing distance of the energized heat generating resistor layer ofthe heater 113 from the contact heating portion N1, so that acontaminant removing ability can be improved. When the movement distanceof the heating unit 112 toward the upstream portion is large, a time(distance) for removing the downstream-side contaminant at the contactheating portion N1 by the fixing roller 110 is increased, so that it ispossible to reliably remove the contaminant located downstream from thecontact heating portion N1.

The frequency of movement of the heating unit 112 in the oppositedirection from the fixing roller rotational direction is not limited toevery printing on one sheet but may also be decreased within the rangeof acceptable amount of the contaminant discharged on the recordingmaterial P. Further, the heating unit may be reciprocated plural timesin the fixing roller rotational direction and the opposite directionthereof during the fixing process of one sheet of the recordingmaterial. That is, the heating member can be reciprocated between thefirst position and the second position during the toner image heating.

The method of moving the heating unit 112 is also not limited to theabove described method using the cam. Similar function and effect can beachieved so long as the heating unit 112 is moved in the oppositedirection from the fixing roller rotational direction when the fixingroller 110 is rotated.

Embodiment 4

In this embodiment, an image forming apparatus for forming an unfixedtoner image is an ordinary image forming apparatus similarly as inEmbodiment 3 and accordingly will not be described in detail. Further,also with respect to the sliding contact type surface image heatingapparatus, members or means identical to those in Embodiment 3 arerepresented by identical reference numerals or symbols and omitted fromexplanation. A constitution of this embodiment is characterized in thata heating element is rotationally moved in a direction opposite from thefixing roller rotational direction at the contact heating portion.

FIG. 19 is a schematic view of a sliding contact type surface imageheating apparatus in this embodiment. The fixing roller 110 and thepressing roller 111 are constituted similarly as in Embodiment 3, sothat the pressing roller 111 is rotated in the arrow R3 direction by therotation of the fixing roller 110 in the arrow R2 direction. A heatingelement 140 for heating the fixing roller 110 contacts an outerperipheral surface of the fixing roller 110 to form a contact heatingportion N3.

The heating element 140 in this embodiment is constituted by a heatroller including an aluminum pipe 143 in which a halogen heater iscontained. On an inner surface of the aluminum pipe 143, a heatinsulating absorbing paint which is liable absorb radiation from thehalogen heater is coated, so that radiant heat is transferred to thealuminum pipe 143. On an outer surface of the aluminum pipe 143, aparting layer of PFA is formed so that paper dust or offset toner comingfrom the fixing roller 110 is less liable to deposit on the aluminumpipe 143. A thinner parting layer is more liable to transfer heat fromthe halogen heater to the outer peripheral surface of the fixing roller110. In this embodiment, the PFA parting layer is formed in a thicknessof 10 μm by coating. As a material for the parting layer 118, inaddition to PFA, a fluorine-containing resin material such as PTFE orFEP may be used but in this embodiment, PFA excellent in heatresistivity and releasability is used. The aluminum pipe 143 candecrease its thermal capacity when it has a small outer diameter and asmall thickness, so that heat is move liable to be quickly transferredto the fixing roller outer surface. However, excessively small outerdiameter and thickness lead to a small (mechanical) strength. When thestrength of the aluminum pipe 143 is lowered, a pressing force forforming the contact heating portion N3 with the fixing roller 110 isless liable to be applied, so that a width of the contact heatingportion N3 is smaller. When the width of the contact heating portion N3is decreased, heat of the heating element 140 is less liable to beconducted to the fixing roller 110, so that a proper strength of thealuminum pipe 143 is required so as to ensure a necessary width of thecontact heating portion N3 in order t shorten a rise time. In thisembodiment, the aluminum pipe 143 has an outer diameter 18 mm and athickness of t=1.0 mm and is pressed against the fixing roller 110 at aforce of 117.6 N in a direction of an indicated arrow A1 by pressingsprings provided at both longitudinal end portions of the aluminum pipe143, thus forming a contact heating portion N3 having a width of 5 mm.

In the contact type surface image heating apparatus using a rotatablemember such as the heat roller as the heating element, generally, theheating element does not slide on the fixing roller and is moved in adirection identical to the rotational direction of the fixing roller atthe contact heating portion but in this embodiment, the surface of theheating element 140 is moved in a direction (arrow R6 direction)opposite from the surface movement direction of the fixing roller 110 atthe contact heating portion N3. A front view as seen from a direction ofan arrow A3 shown in FIG. 19 is shown in FIG. 20. The heating elementhas a shaft 130 at both longitudinal end portions thereof and is pressedagainst the fixing roller 110 in the arrow A1 direction by pressingsprings 129 via bearings 131. At an end of the shaft 130 of the heatingelement, a heating element rotating gear 139 is provided and isrotationally driven by an unshown drive means. As a result, the heatingelement 140 is rotated so that the surface movement direction of theheating element 140 is opposite from the surface movement direction ofthe fixing roller 110, i.e., the arrow R6 direction.

In the case of a conventional roller-shaped surface image heatingapparatus including a heating element containing a halogen lamp andcontacting an outer peripheral surface of a fixing roller, whencontinuous printing is performed, contaminant such as paper dust oroffset toner is deposited on the surface of the heating element in somecases. When the continuous printing is further continued and an amountof the contaminant exceeds a certain value, a large amount of thecontaminant is transferred onto the fixing roller, so that a subsequentrecording material to be conveyed can be contaminated. Further, in somecases, the contaminant at the surface of the heating element iscontinuously grown without being not transferred onto the fixing rollerand heat transfer from heating elements to the fixing roller isinhibited by the contaminant, so that image failure such as fixationfailure is caused to occur.

In the constitution of this embodiment, as described above, the surfaceof the heating element 140 is moved in the opposite direction from thesurface movement direction of the fixing roller 110 at the contactheating portion N3. That is, the heating element 140 is rotated in thesame direction as the rotational direction of the fixing roller 110.FIGS. 21 and 22 are enlarged views of the contact heating portion N3 andits neighborhood. As shown in FIG. 21, even in the case where thecontaminant Y2 is deposited on the heating element 140, the surface ofthe heating element 140 is moved in the opposite direction from thesurface movement direction of the fixing roller 110 (at the contactheating portion N3), so that the contaminant Y2 is removed by rubbing bythe fixing roller 110 as shown in FIG. 22. The contaminant Y2rubbing-removed by the fixing roller 110 can be discharged on therecording material P in the fixing nip N2 similarly as in Embodiment 3.In order to rubbing-remove the contaminant deposited on the heatingelement onto the fixing roller, the heating element surface must bebasically moved in the opposite direction from the fixing roller surfacemovement direction at the contact heating portion. In this embodiment,during the rotation of the fixing roller 110, the heating element 140 isalways rotated in the same direction as the rotational direction of thefixing roller 110, so that the surface of the heating element 140 ismoved all the time in the opposite direction from the surface movementdirection at the contact heating portion N3. In other words, at thecontact heating portion N3, the fixing roller 110 is in such a statethat it always rubs and removes the contaminant on the heating element140, so that it is opposite to suppress deposition of the contaminant onthe heating element 140.

The discharge of the contaminant on the surface of the heating element140 by rotating the heating element 140 in the same direction as therotational direction of the fixing roller 110 is performed onto therecording material P similarly as in Embodiment 3, so that the dischargemay preferably be frequently performed so that the contaminant Y2discharged on the recording material P is unnoticeable. In thisembodiment, when the fixing roller 110 is rotated in the arrow R2direction, the heating element 140 is always rotated (in the arrow R6direction) in conjunction with the rotation of the fixing roller 110.For this reason, the surface contaminant of the heating element 140 isalways rubbed and removed by the fixing roller 110 and can beunnoticeably discharged little by little on the recording material P.

The rotation speed of the heating element 140 relative to that of thefixing roller 110 achieves an effect of transferring the surfacecontaminant of the heating element 140 onto the fixing roller 110 evenat a small value so long as the heating element 140 is rotated but aneffect of rubbing and removing the contaminant on the fixing roller 110is increased with a higher rotation speed. However, when the rotationspeed of the heating element is excessively high, a rotational torquefor rotating the heating element 140 is increased. For this reason, inthis embodiment, the surface movement speed of the heating element 140in the arrow R6 direction is 3 mm/sec.

As described above, according to the constitution of this embodiment, itis possible to unnoticeably discharge the contaminant deposited on theheating element surface little by little on the recording material P byrotating the heating element in the same direction as the fixing rollerrotational direction so that the heating element surface is moved in theopposite direction from the fixing roller surface movement direction atthe contact heating portion. As a result, it is possible to suppress thedeposition of the contaminant on the heating element surface.

By using the above described constitution, a printing durability testwas performed in the same manner as in Embodiment 3. In this embodiment,the heating element is always rotated in the same direction as thefixing roller rotational direction, so that the contaminant reaching thecontact heating portion is always rubbed and removed by the fixingroller, thus being not accumulated on the heating element. As a result,there were no occurrences of image failure and fixation failure due tothe contamination of the heating element even when the test wascontinued up to 10×10⁴ sheets corresponding to the lifetime of the imageforming apparatus.

In the constitution of this embodiment, when the fixing roller 110 isrotated, the rotation of the heating element 140 and the rotation of thefixing roller 110 are performed together so as to always rotate theheating element 140 but the heating element does not have to be alwaysrotated. For example, when the toner on the recording material P isfixed, the heating element is reversely rotated in synchronism with therotation of the fixing roller 110 so as to move the fixing rollersurface and the heating element surface in the same direction. Further,only when the recording material P does not pass through the fixing nipN2, the heating element 140 may be rotated in the same direction as therotational direction of the fixing roller 110 so that the fixing rollersurface movement direction and the heat element surface movement areopposite from each other. As a result, it is possible to reduce therotational torque when the toner on the recording material P is fixed.In addition, by rotating the heating element 140 in the same directionas the rotational direction of the fixing roller 110 when the recordingmaterial P does not pass through the fixing nip P, the contaminant canbe transferred from the fixing roller 110 onto the pressing roller 111,thus being discharged on the back surface of the recording material P.Further, similarly as in Embodiment 3, by frequently performing theabove described rotation operation of the heating element, e.g., everyfixing of toner image on one sheet of the recording material, thecontaminant may be unnoticeably discharged on the back surface of therecording material P. As another method, a mode for cleaning the surfaceof the heating element 140 by removing the contaminant is provided inadvance and in this mode, the heating element 140 may be rotated in thesame direction as the rotational direction of the fixing roller 110 atarbitrary timing by a user or automatically after a predetermined numberof sheets are subjected to the fixing process.

Embodiment 5

In this embodiment, an image forming apparatus for forming an unfixedtoner image is an ordinary image forming apparatus similarly as inEmbodiment 3 and accordingly will not be described in detail. Further,also with respect to the sliding contact type surface image heatingapparatus, members or means identical to those in Embodiment 3 arerepresented by identical reference numerals or symbols and omitted fromexplanation. A constitution of this embodiment is characterized in thata only a heat sliding layer is moved in a direction opposite from thefixing roller rotational direction at the contact heating portion. Inthis embodiment, the heat sliding layer corresponds to the heatingmember.

A schematic view of a sliding contact type surface image heatingapparatus in this embodiment is shown in FIG. 23. The fixing roller 110and the pressing roller 111 are constituted similarly as in Embodiment3, so that the pressing roller 111 is rotated in the arrow R3 directionby the rotation of the fixing roller 110 in the arrow R2 direction. Aheating unit 150 for heating the fixing roller 110 contacts an outerperipheral surface of the fixing roller 110 to form a contact heatingportion N4.

The heating unit 150 in this embodiment is constituted by a heater(hearing element) 132 as a heating source, a heater holder 133 whichholds the heater 132, and a heat sliding layer 134 provided at a portioncontacting the fixing roller 110.

In the constitution of this embodiment, the heat sliding layer 134 ismovable in directions identical to and opposite from the fixing rollerrotational direction and the heater holder 133 for holding the heater132 is immovably fixed to the fixing apparatus. The heater holder 133 ispressed by pressing springs 114 in a direction indicated by an arrow A1with a force of 117.6N to create the contact heating portion N4 having awidth of 8 mm via the heat sliding layer 134. The heat sliding layer 134includes a base metal material excellent in durability and heatconductivity. The base metal material is a 30 μm-thick stainless steel(SUS) sheet, on which surface a parting layer of PFA for suppressing thedeposition of paper dust and toner is formed by coating. In thisembodiment, such a constitution that the heater 132 and the heat slidinglayer 134 are slidably moved together is employed, so that heatresistive silicone grease is applied between the heater 132 and the heatsliding layer 134 in order to decrease a frictional force therebetweenand prevent wearing at a sliding portion. As a means other than thegrease, it is also possible to form a layer of a material such as PTFEor PFA having a good slidability and heat resistivity, as a protectivelayer, at a contact sliding surface between the heater 132 and the heatsliding layer 134. In the case of forming the protective layer, theprotective layer may preferably have a small thickness so as not toinhibit heat conduction from the heater 132 to the fixing roller 110 andmay preferably be formed in a thickness of about 1-50 μm by coating orthe like. The heat sliding layer 134 interposed between the heater 132and the fixing roller 100 receives a frictional force in a directionindicated by an arrow A4 at the contact heating portion N4 when thefixing roller 110 is rotated in the arrow A2 direction. The heat slidinglayer 134 is supported by a heat sliding layer supporting late 135 at anend portion upstream from the contact heating portion N4 in an entirelongitudinal area at the end portion, and the heat sliding layersupporting plate 135 is supported by a heat sliding layer swingable cam136 provided downstream from the heat sliding layer supporting late 135.

A schematic view of the fixing apparatus as seen from the arrow A1direction shown in FIG. 23 is shown in FIG. 24. The cam 136 is providedabout a cam shaft 139 at both longitudinal end portion of the heatsliding layer supporting pate 135. The cam 136 is rotated in a directionindicated by an arrow R7 by rotationally driving a cam rotating gear 137provided at an end of the cam shaft 139 by an unshown driving means. Thecam 136 has the same shape as that of the heat element swingable cam 141in Embodiment 3 and specifically has such a shape that a radius isgradually increased from a minimum radius of 10 mm to a maximum radiusof 14 mm. By rotating the cam 136 in the arrow R7 direction when theheat sliding layer 134 receives a frictional force in an arrow A4direction by rotation of the fixing roller 110 in the arrow R2direction, similarly as in the heating unit 112 in Embodiment 3, theheat sliding layer 134 is reciprocated in directions identical to andopposite from the fixing roller rotational direction.

FIGS. 25 and 26 are enlarged views showing the contact heating portionN4 and its neighborhood, wherein FIG. 25 shows a first position and FIG.26 shows a second position. Even in the case where a contaminant Y3 isdeposited on the heat sliding layer 134 as shown in FIG. 25, when thefixing roller 110 is rotated in the arrow R2 direction, the cam 136 isrotated in the arrow R7 direction and the heat sliding layer 134 ismoved in the opposite direction from the fixing roller rotationaldirection. As a result, as shown in FIG. 26, the contaminant Y3 of theheat sliding layer 134 is rubbed and removed by the fixing roller 110.The contaminant Y3 rubbed and removed by the fixing roller 110 can bedischarged, similarly as in Embodiment 3, on the recording material P inthe fixing nip N2.

The timing of movement of the heat sliding layer 134 and the timing ofconveyance of the recording material P in this embodiment are identicalto those with respect to the heating unit 112 and the recording materialP in Embodiment 3. More specifically, when the recording material Ppasses through the fixing nip N2, the heat sliding layer 134 is alwaysmoved in the opposite direction from the fixing roller rotationaldirection, so that the contaminant Y3 is not accumulated at a portiondownstream from the contact heating portion N4.

In the constitution of this embodiment, it is possible to remove thecontaminant remaining at the contact heating portion N4 by moving onlythe heat sliding layer 134 without moving the heater 132. For thisreason, a center line of the heater 132 and a center line of the fixingroller 110 are not deviated from each other, so that the energized heatgenerating resistor layer of the heater 132 does not come out of thecontact heating portion N4. For this reason, a width of the energizedheat generating resistor layer can be increased up to a width of thecontact heating portion N4. A wider energized heat generating resistorlayer is caused to contact the fixing roller 110 is more liable to heatthe surface of the fixing roller 110, thus shortening a rise time. Inthis embodiment, the width of the energized heat generating resistorlayer of the heater 132 is equal to the width of the contact heatingportion N4 and specifically is 8 mm, so that the surface of the fixingroller 110 can be heated in a shorter time.

By using the above described constitution, a printing durability testwas performed in the same manner as in Embodiment 3. In this embodiment,the heat sliding layer is moved in the opposite direction from thefixing roller rotational direction during the passage of the recordingmaterial through the fixing nip, so that the contaminant reaching thecontact heating portion is always rubbed and removed by the fixingroller, thus being not accumulated on the contact heating portion. As aresult, there were no occurrences of image failure and fixation failuredue to the contamination of the contact heating portion even when thetest was continued up to 10×10⁴ sheets corresponding to the lifetime ofthe image forming apparatus.

Similarly as in Embodiment 3, also in the constitution of thisembodiment, timing, speed, and frequency for moving the heat slidinglayer 134 are not limited to those described above. Further, the methodof moving the heat sliding layer 134 is also not limited to the abovedescribed method using the cam but may also be changed to other methods.Also in these methods, similar function and effect can be achieved solong as the heat sliding layer 134 is moved in the opposite directionfrom the fixing roller rotational direction during the rotation of thefixing roller 110.

Embodiment 6

In this embodiment, an image forming apparatus for forming an unfixedtoner image is an ordinary image forming apparatus similarly as inEmbodiment 3 and accordingly will not be described in detail. Further,also with respect to the sliding contact type surface image heatingapparatus, members or means identical to those in Embodiment 3 arerepresented by identical reference numerals or symbols and omitted fromexplanation.

In the constitution described in Embodiment 5, the heat sliding layer isreciprocated in directions identical to and opposite from the fixingroller rotational direction but in the constitution of this embodiment,a belt-like heat sliding layer is used and similarly as in the case ofthe heating element 140 in Embodiment 4, the surface of the belt-likeheat sliding layer is moved in the opposite direction from the fixingroller surface movement direction to prevent contamination of the heatsliding layer.

FIG. 27 is a schematic view of the fixing apparatus of this embodiment.A heat sliding belt 145 as the heat sliding layer is stretched about abelt guide 146 and a belt rotating roller 147. Similarly as in the caseof the heat sliding layer 134 in Embodiment 5, a base metal material ofthe belt 145 is a 30 μm-thick stainless steel (SUS) belt, on whichsurface a parting layer of PFA for preventing the deposition of paperdust and toner is coated. In this embodiment, such a constitution thatthe heater 132 and the heat sliding belt 145 are slidably moved togetheris employed similarly as in Embodiment 5, so that heat resistivesilicone grease is applied between the heater 132 and the heat slidingbelt 145 in order to decrease a frictional force therebetween andprevent wearing at a sliding portion. As a means other than the grease,it is also possible to form a layer of a material such as PTFE or PFAhaving a good slidability and heat resistivity, as a protective layer,at a contact sliding surface between the heater 132 and the heat slidingbelt 145. In the case of forming the protective layer, the protectivelayer may preferably have a small thickness so as not to inhibit heatconduction from the heater 132 to the fixing roller 110 and maypreferably be formed in a thickness of about 1-50 μm by coating or thelike. The belt rotating roller 147 is formed of foamed silicone rubbersimilarly as in the elastic layer of the fixing roller 110 and isrotated in a direction indicated by an arrow R9 to rotationally move theheat sliding belt 145 in a direction indicated by an arrow R9. Similarlyas in the case of the heating element 140 in Embodiment 4, the rotationsof the fixing roller 110 and the belt rotating roller 147 are performedtogether, so that the heat sliding belt 145 is rotated in the direction(arrow R9 direction) identical to the rotational direction (arrow R2direction) of the fixing roller 110 during the rotation of the fixingroller 110. For this reason, the contaminant reaching the contactheating portion N4 by the printing operation is rubbed and removed bythe fixing roller 110.

In the constitution of this embodiment, during the rotation of thefixing roller 110, the surface of the heating element (heat sliding belt145) is always moved in the opposite direction from the surface movementdirection of the fixing roller 110 similarly as in Embodiment 4, so thatthe surface of the heating element is moved all the time in the oppositedirection from the surface movement direction at the contact heatingportion N4. In other words, at the contact heating portion N3, thefixing roller 110 is in such a state that it always rubs and removes thecontaminant on the heat sliding belt 145, so that it is opposite tosuppress deposition of the contaminant on the heat sliding belt 145.Further, the heat sliding layer is a thin belt, so that it has a smallerthermal capacity than that of the metal pipe in Embodiment 4 and alsohas a flexibility, thus being liable to form a desired width of thecontact heating portion N4. For this reason, heat from the thermalsource is liable to be conducted to the fixing roller 110, so that arise time of the fixing roller 110 can be shortened.

By using the above described constitution, a printing durability testwas performed in the same manner as in Embodiment 3. In this embodiment,the surface of the heat sliding belt 145 is moved always in the oppositedirection from the surface movement direction of the fixing roller 110at the contact heating portion N4, so that the contaminant reaching thecontact heating portion N4 is always rubbed and removed by the fixingroller 110, thus being not accumulated on the heat sliding belt 145. Asa result, there were no occurrences of image failure and fixationfailure due to the contamination of the contact heating portion evenwhen the test was continued up to 10×10⁴ sheets corresponding to thelifetime of the image forming apparatus.

Similarly as in Embodiment 4, also in the constitution of thisembodiment, timing, speed, and frequency for moving the heat slidingbelt 145 are not limited to those described above. Further, the methodof rotating the heat sliding belt 145 in the same direction as thefixing roller rotational direction is also not limited to the abovedescribed method using the driving roller. Also in other equivalentmethods, similar function and effect can be achieved.

In Embodiments 3 to 6 described above, the removal of the contaminant ofthe heating member (or the heating unit) is described. As the pressingmember for forming the fixing nip N2, it is also possible to use anonrotating pad member other than the roller.

Further, the fixing apparatus to be mounted in the image formingapparatus is described in Embodiments 1 to 6 but the present inventionis also applicable to an image heating apparatus such as agloss-imparting apparatus for improving glossiness by re-heating arecording material carrying thereon a toner image which has been fixed.

While the invention has been described with reference to the structuresdisclosed herein, it is not confined to the details set forth and thisapplication is intended to cover such modifications or changes as maycome within the purpose of the improvements or the scope of thefollowing claims.

This application claims priority from Japanese Patent Applications Nos.204238/2006 filed Jul. 27, 2006, 332176/2006 filed Dec. 8, 2006, and184600/2007 filed Jul. 13, 2007, which are hereby incorporated byreference.

1. An image heating apparatus for heating a toner image formed on arecording material, comprising: a roller contactable with a toner imagecarrying surface of the recording material; a heating member for heatingsaid roller, said heating member contacting a surface of said roller,wherein the toner image formed on the recording material is heated incontact with said roller; and a driving mechanism for moving saidheating member to a first position contacting said roller, and a secondposition contacting said roller different from the first position withrespect to a tangential direction of said roller, wherein the secondposition is located upstream from the first position with respect to arotational direction of said roller during heating of the toner image,and wherein said heating member is located at the first position duringthe heating of the toner image and moved from the first position to thesecond position during a period other than a period for the heating ofthe toner image.
 2. An apparatus according to claim 1, wherein saidroller is rotatable normally and reversely and constitutes a part ofsaid driving mechanism, and said heating member is moved to the firstposition or the second position depending on a force exerted thereonfrom said roller.
 3. An apparatus according to claim 1, wherein saiddriving mechanism includes said roller for moving said heating member tothe first position and an urging member for moving said heating memberto the second position.
 4. An apparatus according to claim 3, whereinsaid heating member is moved to the first position against an urgingforce of said urging member by receiving a force from said roller whensaid roller is rotated, and is moved to the second position by theurging force of the urging member when said roller is stopped.
 5. Anapparatus according to claim 1, wherein said heating member is held by aholder and a gap for moving said heating member to the first positionand the second position is provided between said holder and said heatingmember.
 6. An image heating apparatus for heating a toner image formedon a recording material, comprising; a roller contactable with a tonerimage carrying surface of the recording material; a heating member forheating said roller, said heating member contacting a surface of saidroller, wherein the toner image formed on the recording material isheated in contact with said roller; and a driving mechanism for movingsaid heating member to a first position contacting said roller and asecond position, contacting said roller different from the firstposition with respect to a tangential direction of said roller; whereinsaid heating member includes a substrate and a heat generating resistorformed on the substrate and the heat generating resistor is located in acontact area between said heating member and said roller both when saidheating member is located at the first position and when said heatingmember is located at the second position.